Epoxy resin powder coating compositions are widely used for the insulation of electric and electronic equipments and parts. An example is in Japanese Patent Application (OPI) No. 161423/85 (the term "OPI" as used herein refers to a published unexamined Japanese patent application) which discloses a blend of an epoxy resin, a novolak type phenol resin, a butyral resin, and an inorganic filler. Another example is in Japanese Patent Application (OPI) No. 89271/86 which discloses a blend of an epoxy resin, an acid anhydride base hardener, triphenylphosphine, and an inorganic filler. Those powder coating compositions are effective to form insulating coating on smooth surfaces, however, they are not yet satisfactory as insulating powder coating compositions for slots having edges such as in motor rotors and stators of electric and electronic equipment and parts. That is, a temperature of 180.degree. C. or higher is adopted to rapidly harden the epoxy resin to form insulating films on slots having edges, however, the aforesaid conventional epoxy resins under such a temperature condition fail to form films with sufficient thickness on the edge parts and also such physical properties as thermal resistance, adhesibility, and impact strength, are far from sufficient. In addition, surface smoothness is not attained.